Chaining some Timer overloads.

AsyncRx.NET/System.Reactive.Async/System/Reactive/Linq/Operators/Timer.cs

@@ -8,10 +8,7 @@ namespace System.Reactive.Linq
 {
     partial class AsyncObservable
     {
-        public static IAsyncObservable<long> Timer(TimeSpan dueTime)
-        {
-            throw new NotImplementedException();
-        }
+        public static IAsyncObservable<long> Timer(TimeSpan dueTime) => Timer(dueTime, TaskPoolAsyncScheduler.Default);
 
         public static IAsyncObservable<long> Timer(TimeSpan dueTime, IAsyncScheduler scheduler)
         {
@@ -21,10 +18,7 @@ namespace System.Reactive.Linq
             throw new NotImplementedException();
         }
 
-        public static IAsyncObservable<long> Timer(DateTimeOffset dueTime)
-        {
-            throw new NotImplementedException();
-        }
+        public static IAsyncObservable<long> Timer(DateTimeOffset dueTime) => Timer(dueTime, TaskPoolAsyncScheduler.Default);
 
         public static IAsyncObservable<long> Timer(DateTimeOffset dueTime, IAsyncScheduler scheduler)
         {
@@ -34,13 +28,7 @@ namespace System.Reactive.Linq
             throw new NotImplementedException();
         }
 
-        public static IAsyncObservable<long> Timer(TimeSpan dueTime, TimeSpan period)
-        {
-            if (period < TimeSpan.Zero)
-                throw new ArgumentOutOfRangeException(nameof(period));
-
-            throw new NotImplementedException();
-        }
+        public static IAsyncObservable<long> Timer(TimeSpan dueTime, TimeSpan period) => Timer(dueTime, period, TaskPoolAsyncScheduler.Default);
 
         public static IAsyncObservable<long> Timer(TimeSpan dueTime, TimeSpan period, IAsyncScheduler scheduler)
         {
@@ -52,13 +40,7 @@ namespace System.Reactive.Linq
             throw new NotImplementedException();
         }
 
-        public static IAsyncObservable<long> Timer(DateTimeOffset dueTime, TimeSpan period)
-        {
-            if (period < TimeSpan.Zero)
-                throw new ArgumentOutOfRangeException(nameof(period));
-
-            throw new NotImplementedException();
-        }
+        public static IAsyncObservable<long> Timer(DateTimeOffset dueTime, TimeSpan period) => Timer(dueTime, period, TaskPoolAsyncScheduler.Default);
 
         public static IAsyncObservable<long> Timer(DateTimeOffset dueTime, TimeSpan period, IAsyncScheduler scheduler)
         {